Unlike former President Bill Clinton, who was a late and reluctant convert to National Missile Defence, or NMD, Mr Bush argued all through his election campaign that it was vital to set up a system capable of defending America from ballistic missiles fired from countries such as North Korea, Iran and Iraq.

Russian President Putin says the missile defence system will harm international relations

The fact that his Defence Secretary, Donald Rumsfeld, and his Secretary of State, Colin Powell, are both advocates, means that one way or another this is a policy initiative the Bush administration is pursuing with some vigour.

Obstacles for NMD

But there are any number of minefields to be crossed along the way.

Not least is the cost, estimated by the Congressional Budget Office to be in the region of $60bn.

That is on top of the $60bn that has already been spent researching the concept since it was first proposed by the then President Ronald Reagan in the 1980s.

Supporters argue that it is a small price to pay for the foolproof defence of the nation. But so far, NMD has proved to be anything but foolproof.

Two of the first three tests of the systems failed.

A missile defence system would not defend against terrorist acts

And even if it is possible to develop the technology which will in effect shoot a bullet with a bullet (or a laser), you are still left with the problem of how to deal with decoys, multiple launches, or other delivery methods.

With a missile-shield in place, aggressors might simply decide to use alternative delivery systems for their nuclear, chemical or biological warheads - like a truck, or a backpack, or an aerosol can.

But the Bush administration argues that the countries once known as "Rogue States" (before being re-labelled as "States of Concern" by the Clinton team), are all developing longer-range missiles, and it would be negligent not to try to combat the threat.

New arms race?

Of course, combat the threat from them, and you have also gone some way to addressing the potential threat from other countries.

Comments by the Russian President Vladimir Putin that the US deployment of a National Missile Defence shield would do "irreparable damage to the architecture of international relations" indicate just how tough the political battle is likely to be for President George W Bush over this controversial system.

Not only would NMD give the US a strategic edge, it would also break the 1972 Anti Ballistic Missile Treaty signed with the Soviet Union.

Mr Bush has indicated that if the treaty cannot be renegotiated he would scrap it rather than forgo NMD.

Missile defence faces opposition from friends and foes of the US

The Russians suggest that if that happened they would have no choice but to beef up their own armoury.

China appears to feel even more vulnerable to NMD. Because, while the new system would be unable to defend the US from a mass strike by Russia with its estimated 6,000 warheads, China has only about 20 ICBMs, about the size of arsenal that NMD would be designed to combat.

Again, NMD opponents see the ingredients for a dangerous new arms race.

Concern in Europe

The Europeans too are distinctly dubious about US implementation of NMD and are concerned about the impact on relations with Russia.

The Bush administration will have to decide the extent to which is prepared to sacrifice diplomatic friendships and isolate strategic adversaries for the sake of a missile shield, which is not yet proven and which could be quickly rendered obsolete by the development of new weapons or tactics.

But for the Bush administration and its supporters, the alternative is to leave the most powerful nation in the world vulnerable to attack from anyone with a missile, a warhead and a hatred of the United States.